1. Field of the Invention
The present invention generally relates to a method of cleaning semiconductor devices, and more particularly to a method of cleaning semiconductor devices in which contaminants sticking on sidewalls of patterns or trenches are effectively removed or changed in quality. The present invention further relates to apparatus for implementing such a cleaning method.
2. Description of the Background Art
A step of etching process for forming fine interconnection patterns is included in a process for manufacturing semiconductor devices. In this etching process, the plasma etching employing plasma of reactive gas or the reactive ion etching (referred to as "RIE" hereinafter) is widely introduced at present.
FIG. 7 is a schematic view of a conventional RIE apparatus.
Referring to FIG. 7, the processing apparatus has a hollow processing container 10. In processing container 10, a plate high-frequency electrode 11 and a plate high-frequency electrode 12 are provided facing to each other in parallel. An exhaust port 8 for exhausting the gas in the processing container 10 to implement a vacuum condition therein is provided in a lower portion of processing container 10. A gas introducing port 7 for introducing a reactive gas into processing container 10 is provided in the upper portion of processing container 10. One output of a high-frequency power source 13 is directly connected to plate high-frequency electrode 11 provided in the upper portion. The other output of high-frequency power source 13 is connected to plate high-frequency electrode 12 provided in the lower portion through a capacitor 14. A substrate to be treated 4 is located on plate high-frequency electrode 12 provided in the lower portion.
Next, operation for etching an aluminum alloy film to form an interconnection pattern employing the above RIE apparatus will be described.
FIGS. 8A-8C are sectional views showing the steps for forming an interconnection pattern on the semiconductor substrate.
Referring to FIG. 8A, a silicon oxide film 17 is formed on a semiconductor substrate 18. An aluminum alloy film 16 to be an interconnection pattern is formed on silicon oxide film 17. A resist pattern 15 with a pre-determined shape is formed on aluminum alloy film 16.
The obtained substrate to be treated 4, referring to FIG. 7, is located on plate high-frequency electrode 12 provided in the lower portion. Next, chlorine type reactive gas (for example, BCl.sub.3, SiCl.sub.4, Cl.sub.2, CCl.sub.4 etc.) is introduced in processing container 10 through gas introducing opening 7, and in the meanwhile, the gas is exhausted through exhaust port 8. By this operation, the interior of processing container 10 is maintained at a predetermined pressure. In this condition, when high-frequency power source 13 is turned on, a high-frequency voltage is applied between plate high-frequency electrode 11 and plate high-frequency electrode 12. Upon application of the high-frequency voltage, plasma of a chlorine type reactive gas is produced between plate high-frequency electrode 11 and plate high-frequency electrode 12 to form a plasma region 21 in processing container 10. When the above-described condition is implemented in processing container 10, plate high-frequency electrode 12 on which substrate to be treated 4 is carried is negatively charged. Then, a strong electric field region referred to as a sheath region 22 is produced between plasma region 21 and plate high-frequency electrode 12. The velocity at which the reactive ions produced in the plasma advance downwardly is accelerated by the electric field of this sheath region 22 in impinging onto plate high-frequency electrode 12 and substrate to be treated 4. Referring to FIG. 8B, aluminum alloy film 16 is gradually etched by the incident reactive ions to form an interconnection pattern 16a of a condition in which etching is completed, referring to FIG. 8C.
In the above-described steps, referring to FIGS. 8B and 8C, deposition films 19 mainly composed of products of the etching reaction are formed on sidewalls of interconnection pattern 16a. If chlorine type gas such as BCl.sub.3, SiCl.sub.4, Cl.sub.2, CC.sub.4 is employed as a reactive gas, deposition films 19 composed of complicatedly mixed aluminum chloride, carbon, silicon and so forth are formed. If the substrate to be treated 4 in the conditions of FIG. 8C, that is, on which deposition films 14 are formed, is left in the air, a serious problem is produced. This is because, with this deposition film 19 including a large amount of chlorine compounds, the chlorine compounds react with moisture in the air to produce HCl. If HCl is produced on sidewalls of interconnection pattern 16a formed of aluminum alloy, corrosion of the aluminum is produced. The speed of the corrosion is so fast that an interconnection pattern of a width of several .mu.m is cut off only in several minutes in the worst case. Therefore, to prevent this corrosion, it is necessary to sufficiently remove the chlorine compounds sticking on sidewalls of interconnection pattern 6a or change their qualities into other substances which do not cause corrosion.
Next, a conventional method for preventing corrosion of sidewalls of resist patterns will be described.
Referring to FIGS. 8C and 7, after etching, a substrate to be treated 4 is not taken out into the air soon and the gas in processing container 10 is sufficiently exhausted. After that, fluorine type gas such as CF.sub.4 is introduced into processing container 10 through gas introducing opening 7 to produce plasma by a method similar to that in etching. Then, fluorine ions are directed onto the surface of substrate to be treated 4, and the chlorine of the chlorine compounds existing in deposition films 19 is replaced by the fluorine. Once the chlorine in the chlorine compounds is replaced by fluorine, the reaction with the moisture in the air does not produce HCl no longer. Consequently, the interconnection pattern is prevented from corroding.
However, the conventional method for preventing corrosion of sidewalls of resist patterns also employed the plasma processing apparatus provided with parallel plate electrodes shown in FIG. 7, so that it was difficult to directly direct reactive ions onto the sidewalls of resist pattern 16a. The reason thereof will be described next. That is, referring to FIG. 3B, the apparent velocity vector 25 of the reactive ions (CF.sub.3.sup.+) is determined by a sum of the velocity vector 23 of the reactive ions in plasma region 21 and the velocity vector 24 the reactive ions accelerated in the sheath region 22 obtained. While the former velocity vector 23 has random directionality, the latter velocity vector 24 is vertical to substrate to be treated 4. In the RIE, the temperature of the ions in the plasma is low, so that the former is much smaller than the latter, so that the reactive ions vertically impinge onto the surface of substrate to be treated 4. Therefore, ions do not directly impinge on sidewalls of resist pattern 16a. Referring to FIG. 8C, if ions (CF.sub.3.sup.+) do not directly impinge on the sidewalls of resist pattern 16a, removal or change in quality of deposition films 19 is not performed sufficiently. Accordingly, troubles such as cut off of the interconnection pattern as described above have been caused.
As for prior art which relates to the present invention, in Japanese Patent Laying-Open No. 63-117426, a technique of employing electronic cyclotron resonance to produce ultra violet light which is employed to cleaning surfaces of substrates to be treated is disclosed. However, this method also had a problem that contaminants sticking on sidewalls of a resist pattern are not sufficiently removed, as an ultra violet light having the property of going straight is directed to the substrate to be treated.